I passed my PPL back in 1981, and accumulated about 170 hours total time before getting married, buying a house and raising kids got in the way.
In 1999 I resumed flying after about 15 years of only fooling around with Flight Simulator. It took me 15 hours of dual to get it back. In Canada you have to demonstrate to an instructor, after 5 years with no time, that you can successfully pull off all the exercises for the PPL exam; 15 hours was what it took me.
The actual flying skills came back pretty quickly, IMHO if you have about 100 hours that's the "like riding a bicycle" part. What took more time was cockpit procedures, navigation, diversions, etc. Even now, with some 600+ hours, if I don't fly for several months, it's the cockpit drills that are the first to go. We had a terrible winter this year and I was also medically grounded for 3 months which didn't help. I made a point of flying with another pilot until I was back up to speed.
I would think that after 20 years with so few hours, it's pretty much going to be like starting all over again. No point in trying to cut corners. In any case you must demonstrate proficiency to pass the PPL. Having the minimum hours is one thing, but they'll count for nought if you can't pass the PPL, and the time needed for that will pretty quickly become obvious when you start again.